Re: Xeon vs Opteron - second revision - tests and questions

On Fri, Nov 11, 2005 at 08:26:41PM +0100, Marcin Giedz wrote:
> Tom Lane napisa?(a):
>
> >Marcin Giedz <marcin(dot)giedz(at)eulerhermes(dot)pl> writes:
> >
> >
> >>However I still can see 'spikey' performance but not as much as before
> >>changes. What can I do more to eliminate or smooth these spikes?
> >>
> >>
> >
> >The spikes are certainly caused by checkpoints. You can fool with the
> >checkpoint timing via checkpoint_segments and checkpoint_timeout.
> >
> >
> I didn't mention before but I changed checkpoint_segments to 300 but no
> checkpoint_time. Disk space doesn't matter at all ... time to
> recovery.... shouldn't be very long (I don't have much experiences with
> this as I do online backup every day). Can anyone please tell me what
> values of these two parametres are reasonable?

What Tom was refering to about 'time to recovery' is recovering from an
unexpected database shutdown by replaying the WAL. If you go 5 minutes
between syncing WAL to the mainline storage, then a worst-case recovery
will take ~5 minutes (well, it could probably take longer, but it should
be a linear relationship). The longer you make checkpoint interval, the
longer you'll have to wait for the database to come back.
--
Jim C. Nasby, Sr. Engineering Consultant jnasby(at)pervasive(dot)com
Pervasive Software http://pervasive.com work: 512-231-6117
vcard: http://jim.nasby.net/pervasive.vcf cell: 512-569-9461